THE UNUSUAL TELOMERES OF DROSOPHILA

The telomeres of most eukaryotes contain short, simple repeats that are highly conserved. Drosophila, on the other hand does not have such sequences, but carries at the ends of its chromosomes one or more LINE-like retrotransposable elements. Instead of elongation by telomerase, incomplete DNA replication at the termini of Drosophila chromosomes is counterbalanced by transposition of these elements at high frequency specifically to the termini. These transposable elements are not responsible for distinguishing telomeric ends in Drosophila from broken chromosome ends; the structure performing this function is not yet known. Proximal to the terminal army of transposable elements are regions of tandem repeats that are structurally, and probably functionally, analogous to the subterminal regions in other eukaryotes.